Getting Started

1
Getting Started

• In order, list the tasks you performed this
  morning before you left for campus.

2
Programming is a lot like planning out your
morning

• Some things are required, others are optional.
• Certain things must be in the right order while
  other things can be done in any order.
• Certain tasks are MUCH more involved, but we
  think about them from high view simple terms.
• Some tasks you assign to other objects.

3
Programming

• IF, the basic operations of the CPU are those of
  logic, arithmetic, and the rearrangement of
  information in memory
• AND, software is the appropriate combination of
  these simple operations
• THEN

4
Question

• What is the best way write a program?

5
Generations of Programming Languages

• Generation one (early 1940s to the early 1950's )
  -- machine languages
• Generation two (early 1950's to the present) --
  assembly language
• Generation three (middle 1950's to the present)
  -- high-level languages
• Note Many sources will talk about 4GL and 5GL,
  but they dont fit in to this discussion

6
Machine Language

• The native tongue of a computer is machine
  language. Everything is represented by a binary
  string of zeros and ones
• 10110011 00011001
• 01111010 11010000 110010100
• 10011111 00011001
• 01011100 11010001 100100000
• 10111011 11010001 10010110

7
Machine Language

• Early computers required the programmer to set
  switches and move wires
• Which represented a series of 1s and 0s
• Later computers were programmed using punched
  cards

8
Problems with Machine Language

• Coding is quite error prone
• Coding is tedious and slow
• Code is extremely difficult to modify
• Code is not portable to a different type of
  computer

9
Assembly Language

• Assembly language uses Mnemonic symbols to
  represent instructions and data.
• Programmers write programs using symbolic
  operation codes
• MV COST, AB
• MV SHIP, AC
• ADD AC, AB, AD
• STO AD, TOTAL

10
Assembly Language

• To use programs in assembly language
• Write the code in assembly language
• Use an assembler to translate to machine language
• Load and run the machine language version with a
  special program called a loader

11
Problems with Assembly Language

• While assembly language is a little more
  programmer-friendly
• Still tedious
• Still difficult to modify
• Still not portable

12
High-level languages

• Designed to be human friendly, easy to write,
  easy to read, and easy to understand.
• Each instruction corresponds to many instructions
  in machine language.
• total cost ship

13
High-level Languages

• To use programs written in a high-level language
  (HLL)
• Write the code in the HLL (source code)
• Depending on the language
• Use a compiler to translate the source to machine
  language (object code)
• Use an interpreter to simulate a computer that
  understands the HLL and translate each line of
  source into machine language instruction by
  instruction.

14
A compiled language
15
An interpreted language
16
We will use python

• Python is a high-level programming language first
  released by Guido van Rossum in 1991
• Python is a multi-paradigm programming language
  (primarily functional, object oriented and
  imperative) which has a fully dynamic type system
  and uses automatic memory management.
• Python is interpreted, which means you can write
  and execute code dynamically.
• The language has an open, community-based
  development model managed by the non-profit
  Python Software Foundation.

17
Technically, we will use Jython.

• Jython, formerly known as JPython, is an
  implementation of the Python programming language
  written in Java.
• The base Python interpreter is written in C
• While Jythons interpreter is written in Java
• The advantage???
• Because it goes through Java, you can use Javas
  classes

18
What is JES?

• JES is a free integrated development environment
  for doing python (Jython) programming and
  contains some media manipulation classes not part
  of base Python
• From Georgia Tech
• It has several window panes in it
• For creating programs (definitions pane)
• For trying out code (interactions pane)

19
Lets work through Labs 1 and 2

• The rest of class will be somewhat freeform based
  on how things go and what questions you ask. We
  will look at a variety of issues from Labs 1 and
  2 as well as the slides that follow.

20
Number literals

• By default, JES assumes that anything without a
  decimal is an integer.
• 2
• 2
• -5
• -5
• By default, JES assumes that anything with a
  decimal is a floating point number.
• 3.5
• 3.5
• -4.0
• -4.0

21
Math Operators ( / - )

• But on their own, number literals are boring.
• Python, like most languages, provides 6 binary
  mathematical operators
• Here, binary means two numbers
• Addition
• 3 4
• Multiplication
• 3 4
• Division
• 3 / 4
• Subtraction
• 3 4
• Exponents/powers
• 3 4
• Modulo (Remainder)
• 10 2 and 11 2

22
Math Operators Exercise

• How would I perform each of the following in JES
  and what would be the answer?
• Subtract 7 from 9
• Add 7 to 3
• Divide 3 by 2
• Divide 4.6 by 2
• Multiply 5 by 10
• Find the remainder when you divide 10 by 3

23
Why is the result of 3 / 2 1?

• Each value has a type associated with it that
  tells the computer how to interpret the number
• It is an integer, floating point, letter, etc
• The interpreter determines the type
• 3 is an integer
• 3.0 is a floating point number (has a fractional
  part)
• The result of an operation is in the same type as
  the operands
• 3 and 2 are integers so the answer is an integer 1

24
Casting

• There are other ways to solve the problem of 3 /
  2 has a result of 1
• You can make one of the values floating point by
  adding .0
• 3.0 / 2
• 3 / 2.0
• The result type will then be floating point
• Or you can cast one of the values to the
  primitive types float or double
• float( 3 ) / 2
• 3 / float( 2 )
• But not
• float (3/2)

25
Other Funny Math

• What is the result of
• 31.01 0.01
• Where does the extra stuff come from?

26
Other Funny Math

• Remember what we talked about in regards to
  encoding decimals
• 2n 2n-1 2n-2 22 21 20. 2-1 2-2 2-3
  2m-1 2m
• There are a limited number of places you can
  encode.
• Any leftovers get ignored which causes problems
  when you de-code

27
Operator Order

• The default evaluation order is
• Negation
• Exponents
• Multiplication
• Division /
• Modulo (remainder)
• Addition
• Subtraction -
• The default order can be changed
• By using parenthesis
• (3 4) 2 versus 3 4 2

28
Math Operator Order Exercise

• What is the result of
• 2 3 4 5
• Where would you add parentheses to make it clear
  what is happening first
• How do you change it so that 2 3 happens first?
• How do you change it so that it multiplies the
  result of 2 3 and the result of 4 5?